This invention relates generally to wireless communication systems. More specifically, this invention relates to remote repeaters in wireless communication systems and in particular to a method and apparatus for employing in-band signaling for downlink transmission of commands and uplink transmission of status in a wireless system repeater.
As demand increases dramatically for wireless communication services such as Global System for Mobile Communications (GSM), Cellular Mobile Telephone (CMT), and Personal Communication Services (PCS), the operators of such systems are required to serve an increasing number of users. As a result, a type of base station equipment known as a multicarrier broadband Base Transceiver System (BTS) has been developed which is intended to serve a large number of active mobile stations in each cell. Such broadband BTS equipment can typically service ninety-six simultaneously active mobile stations, at a significant cost per channel.
A conventional cellular phone system 100 is shown in FIG. 1. As illustrated in FIG. 1, the cellular phone system 100 includes a plurality of cells 110a, 110b, a mobile unit 120, a plurality of broadband base transceiver stations (BTS) 105a, 105b, dedicated telephone lines 140, a base station controller (BSC) 130, an A interface 150, a Network and Switching Subsystem (NSS) 160 and a landline switched telephone network 170. An Operations and Maintenance Center (OMC) 180 is connected to BSC 130 through a Network Management Interface 190.
The cellular phone system 100 has a fixed number of channel sets distributed among the BTS 105a, 105b serving a plurality of cells 110a, 110barranged in a predetermined reusable pattern. Maximum utilization efficiency of the BTS 105 in densely populated urban environments can be obtained through an efficient frequency reuse scheme, such as that described in U.S. Pat. No. 5,649,292 entitled xe2x80x9cA Method For Obtaining Times One Frequency Reuse in Communication Systemsxe2x80x9d issued to John R. Doner and assigned to AirNet Communications Corporation, who is the assignee of the present application. According to that arrangement, each cell is split into six radial sectors and frequencies are assigned to the sectors in such a manner as to provide the ability to reuse each available frequency in every third cell. Although this frequency reuse scheme is highly efficient, it requires at least two complete multicarrier, broadband base transceiver systems (BTS) to be located in each cell. Such a configuration results in dramatically increased hardware installation costs for each cell.
Returning to FIG. 1, the mobile unit 120, in a cell 110a or 110b, communicates with the BTS 105a or 105b via radio frequency (RF) means, specifically employing one of the fixed number of channels. The BTS 105a, 105b communicate with the BSC 130 via dedicated telephone lines 140. The BSC 130 communicates with the NSS 160 via the A interface 150.
In the cellular phone system 100, the cell areas typically range from 1 to 300 square miles. The larger cells typically cover rural areas, and the smaller cells typically cover urban areas. Cell antenna sites utilizing the same channel sets are spaced by a sufficient distance to assure that co-channel interference is held to an acceptably low level.
The mobile unit 120 in a cell 110a has radio telephone transceiver equipment which communicates with similar equipment in BTS 105a, 105b as the mobile unit 120 moves within a cell or from cell to cell.
Each BTS 105a, 105b relays telephone signals between mobile units 120 and a mobile telecommunications switching office (MTSO) 130 by way of the communication lines 140.
The communication lines 140 between a cell site, 110a or 110b, and the MTSO 130, are typically T1 lines. The T1 lines carry separate voice grade circuits for each radio channel employed at the cell site and data circuits for switching and other control functions.
While the cellular communications system arrangement of FIG. 1 is cost effective to deploy when a large number of active mobile stations is expected in each cell, it is not particularly cost effective in most other situations. For example, during an initial system build out phase, a service provider ordinarily does not need to use a large number of radio channels. It is therefore typically not possible to justify the cost of deploying complex multicarrier broadband transceiver, system equipment based only upon the initial number of subscribers. As a result, the investment in conventional broadband multicarrier radio equipment may not be justified until such time as the number of subscribers increases to a point where the channels are busy most of the time. Furthermore, many areas exist where the need for wireless communication systems is considerable, but where signal traffic can be expected to remain low indefinitely (such as in rural freeway locations or large commercial/industrial parks). Because only a few cells at locations of high traffic demand (such as in a downtown urban location or a freeway intersection) will justify the initial expense of building out a network of high capacity broadband transceiver systems, the service provider is faced with a dilemma. He can build-out the system with less expensive narrowband equipment initially, to provide some level of coverage, and then upgrade to the more efficient equipment as the number of subscribers rapidly increases in the service area. However, the initial investment in narrowband equipment is then lost. Alternatively, a larger up front investment can be made to deploy the high capacity equipment at the beginning, so that once demand increases, the users of the system can be accommodated without receiving busy signals and the resultant blocked calls. But this has the disadvantage of requiring a larger up-front investment.
These concerns have led to the increased popularity of wireless repeaters, which can increase the capacity of cells without requiring the expense or complication of a multicarrier broadband BTS for each cell. FIG. 2 is a block diagram of the components of a wireless communication system that makes use of wireless repeaters.
FIG. 2 illustrates a wireless communication system 200 such as a Cellular Mobile Telephone, Personal Communication System (PCS), or similar system in which employing slot-by slot diversity selection in the uplink signal paths of a wireless system repeater translator enables proper demodulation at the BTS of signals received from remote repeater base stations deployed in peripheral cells.
The system 200 provides voice and or data communication between mobile stations 210 and a Public Switched Telephone Network (PSTN) (not shown) via radio signals. In the particular embodiment of the invention being described, the radio signaling protocol, or xe2x80x9cair interface,xe2x80x9d uses a Time Division Multiple Access (TDMA) technique such as the GSM-1900 (formerly PCS-1900) standard promulgated by the Telecommunications Industry Association (TIA) in the United States which adopts all relevant aspects of the Global System for Mobile Communication (GSM) standard developed by the Groupe Special Mobile, and promulgated in Europe and elsewhere by the European Telecommunication Standards Institute (ETSI).
The remotely located repeaters 220-1, 220-2, . . . , 120-n (also referred to herein as the xe2x80x9cremote base stationsxe2x80x9d) are each located in what is normally to be approximately the center of a group or cluster 240 of cells comprising individual cell sites 250-1, 250-2, . . . , 250-n. The remotely located repeaters 220 receive radio signals from the mobile stations 210 located in their respective,cells 250 and forward these signals to the associated multichannel host broadband Base Transceiver System (BTS) 260. Likewise, radio signals originating at the host BTS 260 are forwarded by the repeaters 220 to the mobile stations 210. As a result, the signals associated with all of the mobile stations 210 located within the cluster 240 of cells 250-1, . . . , 250-n are thereby processed at the host BTS 150.
The remotely located repeaters 220 can be used to extend the coverage of a single cell, or they can be configured as xe2x80x9cbase stationsxe2x80x9d in the sense that they are each associated with a particular cell 250 and in that they each receive and transmit multiple signals from and to the mobile stations 210. However, the remotely located repeaters 220 do not perform demodulation and modulation functions as does a conventional base station. Rather, in their most basic form, they serve only to amplify signals received from the mobile stations 210 and then direct such signals to the multichannel host BTS 260. More complex versions of remote repeaters perform frequency translation as well as amplification of the signals received from the mobile stations 210, and subsequently direct those amplified and translated signals on a different frequency to the multichannel host BTS 260. When the frequencies employed by the remote repeaters 220 are all within the frequency band allocated to the cell cluster 240, the repeaters 220 are considered xe2x80x9cin-bandxe2x80x9d frequency-translating repeaters. The remotely located repeaters 220 also perform the inverse function, receiving signals from the host BTS 260 and then directing them to the mobile stations 210, including frequency translation.
Also shown in FIG. 2, the multichannel host BTS 260 is connected to a Base Station Controller 270 through an A Interface 280, and the BSC 270 is connected to an Operations and Maintenance Center (OMC) 290 through a Network Management Interface 295. In any conventional wireless communications system, whether it employs remotely located repeaters or not, the OMC 290 receives alarms and status-indicating signals from and sends commands to the base stations, whether they are representative of a multichannel host BTS 260 or a remotely located repeater base station 220. The OMC 290 typically communicates with several base station controllers 270.
In the wireless communications systems of the prior art, in order to conduct such two-way communications between the remote repeaters 220 and the OMC 290, a dedicated telephone line is required. Even in the case where the OMC 290 is physically co-located with the Base Station Controller 270, such an installation requires that a modem be installed in the remote repeater 220, and that telephone line installation and subscription and maintenance charges be incurred. These charges can be substantial, considering that a single OMC 290 can communicate with several BSCs 270. Whereas remotely located wireless repeaters 220 use RF backhaul signals to communicate with a host BTS 260, landline repeaters are connected to a host BTS by a wireline connection. Landline repeaters have successfully employed a solution to the problem of, status-indicating signal and alarm monitoring. U.S. Pat. No. 5,422,929 (""929) to Hurst et al. describes a method and apparatus for remotely testing and monitoring a landline repeater. A central office will send an interrogating signal with an address subfield. When the interrogating signal is recognized by a controller in the landline repeater, the controller causes the landline repeater to enter a loopback mode where diagnostic and test-indicative no-operation signals are returned. For a given landline, any repeater attached to the landline could be addressed and tested. Although ""929 describes the testing and monitoring for landline repeaters through the existing landline communication channel, ""929 does not describe the testing and monitoring through a wireless communication channel and testing of the uplink and downlink paths of a wireless repeater.
U.S. Pat. No. 5,785,406 (""406) to DeJaco et al. describes a method and apparatus for testing through a wireless communication channel. In the ""406 patent, a test signal is generated from a monitoring station located on a PSTN. The test signal is routed through the PSTN to a cellular communication system to a cellular phone. The test signal activates a loopback element within the cellular phone and the signal is re-routed back to the monitoring station. The monitoring station performs an analysis on the returned test signal.
Although the ""406 patent describes the use of the loopback element in a mobile cellular phone through a wireless communication channel, ""406 fails to disclose this loopback element for a wireless repeater. Furthermore, ""406 fails to disclose how to implement this testing for a repeater and for testing the uplink and downlink paths of the wireless repeater.
It is thus readily seen that a need exists for a method of transmitting signals and for monitoring status-indicating signals and alarms between the OMC 290 and multiple remote repeater stations 220 without requiring the installation and use of modems and dedicated telephone lines.
It is an object of this invention to provide wireless signaling between an Operations and Maintenance Center and multiple remotely located repeater stations.
Another object is to provide for wireless downlink transmission of commands from an Operations and Maintenance Center to multiple remotely located repeater stations.
A further object is to provide for wireless uplink transmission of status and alarm signals to an Operations and Maintenance Center from multiple remotely located repeater stations.
It is yet another object of this invention to conduct such wireless signaling in-band, via the downlink and uplink RF paths.
Briefly, the invention is predicated on an architecture for a wireless communication system in which cells are grouped into clusters. A host cell location is identified within each cluster and a multicarrier broadband Base Transceiver System (BTS) is located at or near the host cell site.
Rather than deploy a complete suite of base station equipment at each remaining cell in the cluster, translating radio transceivers are located in the remote cells. In a preferred embodiment of the present invention, these translating radio transceivers operate in-band, that is, within the frequencies assigned to the service provider.
The repeaters operate in both an uplink and downlink direction. That is, uplink signals transmitted by a mobile station located in a remote cell are received at the repeater and then transmitted to the host BTS. Likewise, downlink signals transmitted by the host BTS are first received by the repeater and then transmitted to the mobile stations at high power.
The remotely located repeater has frequency shift key (FSK) detection and demodulation capability incorporated in the downlink path, while it also has FSK modulation capability incorporated in the uplink path. This allows for the repeater to, extract commands from the serving BTS downlink and act upon them. It also allows for the repeater to transmit status/alarms back to the serving BTS via the uplink. The BTS can then communicate these commands, status-indicating signals, and alarms with the Operations and Maintenance Center.
During normal operation, a modulated Gaussian Minimum Shift Key (GMSK) carrier from the BTS is continuously transmitted in the xe2x80x9cbackhaulxe2x80x9d downlink to the remotely located repeater. This signal is received by the repeater via a directional antenna, and transmitted via an omni-directional antenna to the mobile handset. The signal transmitted from the repeater to the mobile unit is referred to as the remote xe2x80x9cgroundxe2x80x9d downlink signal.
The handset returns its signal via the remote xe2x80x9cgroundxe2x80x9d uplink path to the repeater, where it is typically received via two omnidirectional antennas. In the preferred embodiment, the repeater performs diversity selection and automatic level control (ALC) either through delay diversity combining or on a slot-by-slot switched diversity basis. This uplink signal is transmitted to the BTS via a directional antenna.
When an RF loopback test is desired, a xe2x80x9csignaling waveform,xe2x80x9d such as a continuous wave (CW) tone, is transmitted over the xe2x80x9cbackhaulxe2x80x9d downlink from the BTS to the remotely located repeater for a pre-determined amount of time. Phase/frequency discrimination circuitry is used to detect the change to a signaling waveform (e.g. CW carrier) from a modulated carrier, e.g. GMSK. The presence of the signaling waveform instructs the repeater to enter its RF loopback mode.
When in the RF loopback mode, a coupled sample of the high-power downlink transmit signal is attenuated, downconverted in frequency to the receive band, and coupled into both of the uplink low-noise input receive paths. The downlink backhaul carrier from the BTS is then modulated with xe2x80x9ctraining bitxe2x80x9d data to allow for accurate timing of the round-trip delay and path loss when the RF loopback signal is received over the uplink backhaul by the BTS. In the event of an alarm condition within any function of the repeater, the signal will not be looped back to the BTS and a system alarm will be directed to the Operations and Maintenance Center.
While the repeater is ,in the Loopback mode, the phase/frequehcy discrimination circuitry can also be used to detect phase/frequency-modulated downlink data (such as FSK) and the detected data bits can be interpreted by the repeater""s microcontroller and acted upon. The downlink data can be used to re-configure various tuning frequency and target gain parameters.
Further, while the repeater is in the Loopback mode, the status-indicating and alarm data can also be sent back via the uplink path to the BTS. A simple phase/frequency modulation component can be switched or coupled into the uplink path and used to FSK-modulate data supplied by the repeater""s microcontroller. This data can include internal status and alarm signals monitored by the repeater""s microcontroller.